Evol Ecol Res 8: 515-527 (2006)     Full PDF if your library subscribes.

Heightened phenotypic variation and age-based fading of ultraviolet butterfly wing coloration

Darrell J. Kemp*

School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA and Department of Zoology, Stockholm University, SE-10691 Stockholm, Sweden

Address all correspondence to Darrell Kemp, School of Tropical Biology, James Cook University, Cairns, QLD 4870, Australia.
e-mail: darrell.kemp@jcu.edu.au


Hypothesis: Structural coloration (iridescent ornamentation) should vary more greatly among individuals and with age than pigment coloration. Structural coloration requires nano-scale precision and might thus more honestly signal male age and condition than pigment-based colours.

Organism: A natural population of the orange sulphur butterfly, Colias eurytheme. C. eurytheme females prefer young males, choosing them on the basis of an unknown signal.

Site: Cultivated alfalfa (Medicago sativa) fields near Avondale, Arizona, August–September 2004.

Methods: I randomly sampled 70 ‘pristine’ males and an additional 98 males in five age classes. I then measured key reflectance characteristics (brightness, hue and chroma) of the dorsal structural ultraviolet markings and of the coincident pigmentary yellowish-orange.

Conclusions: Consistent with the sexual selection hypothesis, structural reflectance parameters are more phenotypically variable. Structural reflectance also fades more with age. However, the higher phenotypic variance of structural colour renders it a less precise indicator of male age than pigment colour.

Keywords: age, Colias eurytheme, iridescence, Lepidoptera, mate choice, sexual selection.

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